When using a telephone, hearing-impaired people need to have the volume of sound as well as the corresponding frequencies customized to their individual hearing loss in order to provide maximum intelligibility of incoming speech. One way of customizing the sound for a particular hearing-impaired person is to "pre-subscribe" a selected frequency enhancement for a household. In this manner, anytime a telephone extension within the household is used to place or receive a telephone call, the preselected frequency enhancement will be in effect. The hearing impaired person can then receive the benefits of selective frequency enhancement and better intelligibility.
While presubscription to a selected frequency enhancement or "sound flavor" improves intelligibility for the hearing-impaired person, this method of selecting a sound flavor may inconvenience and annoy other members of the household. For example, if the household is occupied by a person with severe hearing impairment to high frequencies, the telephone system can be configured to enhance greatly the high frequency sound components for all telephone calls to the household. However, the other members of the household will then be forced to hear these enhanced high frequency components on each and every call. In another example, a given household may be occupied by two hearing-impaired persons, each of whom requires a different or perhaps opposite frequency enhancement. In this case, presubscription to a particular sound flavor may be entirely inadequate for one of the parties.